1 A Brief History of Microbiology

The Early Years of Microbiology What Does Life Really Look Like? Antoni van Leeuwenhoek Began making and using simple microscopes Often made a new microscope for each specimen Examined water and visualized tiny animals, fungi, algae, and single-celled protozoa; "animalcules" By end of 19th century, these organisms were called microorganisms

Figure 1.2 Reproduction of Leeuwenhoek's microscope. Lens Specimen holder 3

The Early Years of Microbiology How Can Microbes Be Classified? Carolus Linnaeus developed taxonomic system for naming plants and animals and grouping similar organisms together Leeuwenhoek's microorganisms now grouped into six categories as follows: Bacteria Archaea Fungi Protozoa Algae Small multicellular animals

The Early Years of Microbiology How Can Microbes Be Classified? Bacteria and Archaea Unicellular and lack nuclei Much smaller than eukaryotes Found everywhere there is sufficient moisture; some isolated from extreme environments Reproduce asexually Bacterial cell walls contain peptidoglycan; some lack cell walls Archaeal cell walls composed of polymers other than peptidoglycan

Prokaryotic Nucleus of bacterial cells eukaryotic cheek cell Figure 1.4 Cells of the bacterium Streptococcus (dark blue) and two human cheek cells. Prokaryotic bacterial cells Nucleus of eukaryotic cheek cell 6

The Early Years of Microbiology How Can Microbes Be Classified? Fungi Eukaryotic (have membrane-bound nucleus) Obtain food from other organisms Possess cell walls Include Molds – multicellular; grow as long filaments; reproduce by sexual and asexual spores Yeasts – unicellular; reproduce asexually by budding; some produce sexual spores

Hyphae Spores Budding cells Figure 1.5 Fungi. Hyphae Spores Budding cells 8

The Early Years of Microbiology How Can Microbes Be Classified? Protozoa Single-celled eukaryotes Similar to animals in nutrient needs and cellular structure Live freely in water; some live in animal hosts Asexual (most) and sexual reproduction Most are capable of locomotion by Pseudopods – cell extensions that flow in direction of travel Cilia – numerous short protrusions that propel organisms through environment Flagella – extensions of a cell that are fewer, longer, and more whiplike than cilia

Figure 1.6 Locomotive structures of protozoa. Nucleus Pseudopods Cilia Flagellum 10

The Early Years of Microbiology How Can Microbes Be Classified? Algae Unicellular or multicellular Photosynthetic Simple reproductive structures Categorized on the basis of pigmentation and composition of cell wall

Figure 1.7 The structure of nucleic acids. 12

The Early Years of Microbiology How Can Microbes Be Classified? Other organisms that microbiologists study Parasites Viruses

Figure 1.8 An immature stage of a parasitic worm in blood. Red blood cell 14

Virus Bacterium Viruses assembling inside cell Figure 1.9 A colorized electron microscope image of viruses infecting a bacterium. Virus Bacterium Viruses assembling inside cell 15

The Golden Age of Microbiology Scientists searched for answers to four questions Is spontaneous generation of microbial life possible? What causes fermentation? What causes disease? How can we prevent infection and disease?

The Golden Age of Microbiology Does Microbial Life Spontaneously Generate? Some philosophers and scientists of the past thought living things arose from three processes Asexual reproduction Sexual reproduction Nonliving matter Aristotle proposed spontaneous generation Living things can arise from nonliving matter

The Golden Age of Microbiology Does Microbial Life Spontaneously Generate? Redi's experiments When decaying meat was kept isolated from flies, maggots never developed Meat exposed to flies was soon infested As a result, scientists began to doubt Aristotle's theory

Figure 1.10 Redi's experiments. 19

The Golden Age of Microbiology Does Microbial Life Spontaneously Generate? Needham's experiments Scientists did not believe animals could arise spontaneously, but believed microbes could Needham's experiments with beef gravy and infusions of plant material reinforced this idea

The Golden Age of Microbiology Does Microbial Life Spontaneously Generate? Spallanzani's experiments Concluded that Needham failed to heat vials sufficiently to kill all microbes or had not sealed vials tightly enough Microorganisms exist in air and can contaminate experiments Spontaneous generation of microorganisms does not occur Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed the "life force"

The Golden Age of Microbiology Does Microbial Life Spontaneously Generate? Pasteur's experiments When the "swan-necked" flasks remained upright, no microbial growth appeared When the flask was tilted, dust from the bend in the neck seeped back into the flask and made the infusion cloudy with microbes within a day

Figure 1.12 Pasteur's experiments with "swan-necked flasks." 23

The Golden Age of Microbiology Does Microbial Life Spontaneously Generate? The scientific method Debate over spontaneous generation led in part to development of scientific method Observation leads to question Question generates hypothesis Hypothesis is tested through experiment(s) Results prove or disprove hypothesis Accepted hypothesis leads to theory/law Disproved hypothesis is rejected or modified

Figure 1.13 The scientific method, which forms a framework for scientific research. 25

The Golden Age of Microbiology What Causes Fermentation? Spoiled wine threatened livelihood of vintners Some believed air caused fermentation; others insisted living organisms caused fermentation Vintners funded research of methods to promote production of alcohol and prevent spoilage during fermentation This debate also linked to debate over spontaneous generation

The Golden Age of Microbiology What Causes Fermentation? Pasteur's experiments Led to the development of pasteurization Process of heating liquids just enough to kill most bacteria Began the field of industrial microbiology Intentional use of microbes for manufacturing products

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The Golden Age of Microbiology What Causes Fermentation? Buchner's experiments Demonstrated fermentation does not require living cells Showed enzymes promote chemical reactions Began the field of biochemistry

The Golden Age of Microbiology What Causes Disease? Pasteur developed germ theory of disease Robert Koch studied causative agents of disease (etiology) Anthrax Examined colonies of microorganisms

The Golden Age of Microbiology What Causes Disease? Koch's experiments Simple staining techniques First photomicrograph of bacteria First photomicrograph of bacteria in diseased tissue Techniques for estimating CFU/ml Use of steam to sterilize media Use of Petri dishes Techniques to transfer bacteria Bacteria as distinct species

Figure 1.16 Bacterial colonies on a solid surface (agar). Bacterium 6 Bacterium 7 Bacterium 5 Bacterium 8 Bacterium 4 Bacterium 9 Bacterium 3 Bacterium 10 Bacterium 2 Bacterium 11 Bacterium 1 Bacterium 12 32

The Golden Age of Microbiology What Causes Disease? Koch's postulates Suspected causative agent must be found in every case of the disease and be absent from healthy hosts Agent must be isolated and grown outside the host When agent is introduced into a healthy, susceptible host, the host must get the disease Same agent must be found in the diseased experimental host

Figure 1.17 Results of Gram staining. Gram-positive Gram-negative 34

The Golden Age of Microbiology How Can We Prevent Infection and Disease? Semmelweis and handwashing Lister's antiseptic technique Nightingale and nursing Snow – infection control and epidemiology Jenner's vaccine – field of immunology Ehrlich's "magic bullets" – field of chemotherapy

Figure 1.19 Some of the many scientific disciplines and applications that arose from the pioneering work of scientists just before and around the time of the Golden Age of Microbiology. 36

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The Modern Age of Microbiology What Are the Basic Chemical Reactions of Life? Biochemistry Began with Pasteur's work on fermentation and Buchner's discovery of enzymes in yeast extract Kluyver and van Niel – microbes used as model systems for biochemical reactions Practical applications Design of herbicides and pesticides Diagnosis of illnesses and monitoring of patients' responses to treatment Treatment of metabolic diseases Drug design

The Modern Age of Microbiology How Do Genes Work? Microbial genetics Molecular biology Recombinant DNA technology Gene therapy

The Modern Age of Microbiology How Do Genes Work? Microbial genetics Avery, MacLeod, and McCarty determined genes are contained in molecules of DNA Beadle and Tatum established that a gene's activity is related to protein function Translation of genetic information into protein explained Rates and mechanisms of genetic mutation investigated Control of genetic expression by cells described

The Modern Age of Microbiology How Do Genes Work? Molecular biology Explanation of cell function at the molecular level Pauling proposed that gene sequences could Provide understanding of evolutionary relationships and processes Establish taxonomic categories to reflect these relationships Identify existence of microbes that have never been cultured Woese determined cells belong to bacteria, archaea, or eukaryotes Cat scratch disease caused by unculturable organism

The Modern Age of Microbiology How Do Genes Work? Recombinant DNA technology Genes in microbes, plants, and animals manipulated for practical applications Production of human blood-clotting factor by E. coli to aid hemophiliacs Gene therapy Inserting a missing gene or repairing a defective one in humans by inserting desired gene into host cells

The Modern Age of Microbiology What Role Do Microorganisms Play in the Environment? Bioremediation uses living bacteria, fungi, and algae to detoxify polluted environments Recycling of chemicals such as carbon, nitrogen, and sulfur

The Modern Age of Microbiology How Do We Defend Against Disease? Serology The study of blood serum Von Behring and Kitasato – existence in the blood of chemicals and cells that fight infection Immunology The study of the body's defenses against specific pathogens Chemotherapy Fleming discovered penicillin Domagk discovered sulfa drugs

Fungus colony (Penicillium) Zone of inhibition Bacteria Figure 1.20 The effects of penicillin on a bacterial "lawn" in a Petri dish. Fungus colony (Penicillium) Zone of inhibition Bacteria (Staphylococcus) 46

The Modern Age of Microbiology What Will the Future Hold? Microbiology is built on asking and answering questions The more questions we answer, the more questions we have